1. Field of the Invention
The present invention relates to a machine tool having a number of tools for successively performing a plurality of different kinds of operations under the control of a computer.
2. Description of the Prior Art
Conventionally, when a working program for a numerically controlled machine tool was written all of the process data including the types of tools to be used, the sequence of operations to be performed in the preworking and final working steps, and the working dimensions, etc., obtained by analyzing the preworking steps from a planning drawing had to be entered into a computer in order to determine the tools necessary from the initial preworking step to the final working step. The selection of tools was made on the basis of the kind and shape of the final working operations shown in the planning drawing, Thus, it was very troublesome and time-consuming to enter the working program into a computer.
Further, in a conventional numerically controlled machine tool, cutting conditions had to be entered for every kind of operation in order to enter a working program into a numerical control device. This was necessary after reading out a preworking step and a final working step from a final working shape shown in a planning drawing and after determining the kind of operation required for each working step. Thus, a large volume of complicated data on cutting conditions was required and had to be entered repeatedly. Thus, not only has the entering operation of the cutting conditions been troublesome but also there has been a risk of misentering the data.
Japanese Patent Unexamined Publication No. 46408/1983 discloses a method in which working programs are set corresponding to working shapes of a workpiece. This enables cutting conditions stored in advance corresponding to numerical values of the respective working shapes to be read out to perform operations on the workpiece on the basis of the read-out cutting conditions. Since the working shapes of a workpiece vary extremely in kind, in practice it is not possible to store in advance the cutting conditions corresponding to the numerical values of all of the working shapes.
Furthermore, in a conventional machine tool provided with an automatic tool changing device, it has been necessary to preselect the tools that would be used through the working steps from the beginning step to the final working step as shown in the planning drawings. These preselected tools were mounted in a tool magazine, the positions of the tools within the magazine were determined, and the mounted positions of the tools in the tool magazine were entered into the control computer for every step in the working program. Thus, it has been necessary to consider the working, tools and the mounted positions thereof when making a working program. This further made the generating of the working program troublesome and it was difficult to determine in advance the kinds and shapes of the tools needed for all the working steps and to mount all the tools properly in a tool magazine, this further increased the risk of making errors.
Moreover, conventionally, in making a working program for a numerically controlled machine tool, in the case where final working (second working) illustrated in a planning drawing required hole preparation, e.g., tap working or reamer working, or the like, a programmer had to determine the depth of a hole to be made by first working operation. This included consideration of tool diameter, pitch, and the like, so as to enter the depth of the prepared hole in the working program every time the program was made. This contributed to the difficulty of developing the working program.